One more place: admin/options.php:296
If you just want to try another theme, there is no need to uninstall this theme. Simply activate the other theme in the Appearance > Themes admin page.
And the following line, as well:
Note that uninstalling this theme does not remove the theme's files. To delete the files after you have uninstalled this theme, go to Appearances > Themes and delete the theme from there.